You would like to freeze a surgically removed 5.0 cm diameter spherical brain tumor. in order to avoid the formation of large ice crystals within the tumor, you would like to keep the temperature within the tumor spatially uniform. tissue properties: constant thermal conductivity = 0.64 w/m*k, thermal diffusivity = 2.5 x 10-7 m2/s. (a) determine an appropriate h in order to meet this criteria. (b) how long will the tumor take to freeze, i. e. reach 0°c, if placed in a -20°c freezer using the h found in part (a).